When etching a silicon oxide film (SiO2) as a typical insulating material of a semiconductor device in a plasma ambient by dry etching, for example, a gas mixture mainly containing a carbon fluoride compound is often used. When forming a contact hole in SiO2, a gas mixture obtained by adding O2 and an inert gas to a carbon fluoride compound having a high carbon ratio such as C4F8 is used. Consequently, a high selectivity of, e.g., 10 is obtained against silicon (Si).
On the other hand, when etching silicon (Si) in a plasma ambient, a gas mixture mainly containing hydrogen bromide is often used. When forming an Si trench by using SiO2 as a mask, a gas mixture of HBr and O2 is used. As a consequence, a high selectivity of, e.g., 90 is obtained against SiO2.